Levothyroxine comes in 12 tablet strengths: 25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200, and 300 mcg. Most adults on full replacement therapy end up somewhere between 75 and 150 mcg per day, though the range extends well beyond that in both directions depending on body weight, age, and how much thyroid function remains.
How the Right Dose Is Calculated
The standard full replacement dose for adults is roughly 1.6 to 1.7 mcg per kilogram of body weight per day. For a 150-pound person, that works out to about 109 to 116 mcg daily. But that number assumes you have essentially no working thyroid tissue. If your thyroid still produces some hormone on its own, your dose will be lower.
Not everyone starts at their full calculated dose. Younger, otherwise healthy adults can often begin at or near the target. Older adults and people with heart disease start much lower, typically 12.5 to 25 mcg per day, because a sudden increase in thyroid hormone can strain the cardiovascular system. The dose is then raised in small increments of 12.5 to 25 mcg every four to six weeks, with blood work checked each time, until levels normalize.
People with mild or subclinical hypothyroidism, where TSH is elevated but thyroid hormone levels are still in range, often need smaller doses than those with full-blown hypothyroidism. Treatment is generally recommended when TSH rises above 10 mIU/L, and strongly considered at levels above 7 or 8 mIU/L because roughly 70% of people at that level progress to overt hypothyroidism within four years.
Available Tablet Strengths and Colors
Each levothyroxine strength has a standardized color, which helps you and your pharmacist quickly verify you have the correct dose. The color system is consistent across most manufacturers:
- 25 mcg: orange
- 50 mcg: white
- 75 mcg: violet
- 88 mcg: olive green
- 100 mcg: yellow
- 112 mcg: rose
- 125 mcg: brown
- 137 mcg: turquoise
- 150 mcg: blue
- 175 mcg: lilac
- 200 mcg: pink
- 300 mcg: green
This many options exist because even small dose changes, as little as 12 to 25 mcg, can meaningfully shift your thyroid levels. The tight spacing between strengths (75, 88, 100, 112) lets your prescriber fine-tune without over- or under-shooting.
Pediatric Doses
Children need significantly more levothyroxine per kilogram than adults because their metabolism and growth demands are higher. Newborns require the most, at 10 to 15 mcg per kilogram per day, and the per-weight dose decreases steadily as they grow:
- 0 to 3 months: 10 to 15 mcg/kg/day
- 3 to 6 months: 8 to 10 mcg/kg/day
- 6 to 12 months: 6 to 8 mcg/kg/day
- 1 to 5 years: 5 to 6 mcg/kg/day
- 6 to 12 years: 4 to 5 mcg/kg/day
- Over 12 years: 2 to 3 mcg/kg/day
Once growth and puberty are complete, the dose settles to the adult range of about 1.7 mcg/kg/day. For children with severe or longstanding hypothyroidism, starting at one-quarter of the target dose and increasing weekly helps avoid hyperactivity and other adjustment symptoms.
Dose Changes During Pregnancy
Thyroid hormone demand rises substantially during pregnancy. The American Thyroid Association recommends increasing levothyroxine by 20 to 30% as soon as pregnancy is confirmed. A simple way to do this: take two extra doses per week on top of the usual daily schedule. For example, if you normally take one tablet daily, you’d take a second tablet on two days of the week. TSH is then monitored throughout pregnancy and the dose adjusted as needed, with a return to the pre-pregnancy dose after delivery.
For women planning pregnancy, treatment thresholds are also lower. Levothyroxine is generally advised if TSH exceeds 2.5 mIU/L, especially in the presence of thyroid antibodies, even though that level wouldn’t typically trigger treatment outside of pregnancy.
How Dose Adjustments Work Over Time
After any dose change, it takes four to six weeks for your body to reach a new steady state. Checking TSH before that point gives misleading results. The typical adjustment pattern looks like this: start at an initial dose, recheck TSH at four to six weeks, increase by 12.5 to 25 mcg if needed, and repeat until TSH lands in the target range. For most people, this process takes two to four cycles before the dose stabilizes.
Once you’re on a stable dose, TSH is typically rechecked every 6 to 12 months. Your dose may need revisiting if your weight changes significantly, you start or stop certain medications, you age into your 60s or 70s (when requirements often decrease), or you develop new health conditions.
Timing and Absorption
Levothyroxine is best absorbed on an empty stomach. The standard recommendation is to take it 30 to 60 minutes before eating. Calcium supplements, iron supplements, and antacids can block absorption and should be separated by at least four hours.
Coffee has traditionally been flagged as a concern, but recent research from the Endocrine Society found that the liquid formulation of levothyroxine taken five minutes before coffee (black, without milk) was absorbed just as well as under fasting conditions. For tablet formulations, the 30 to 60 minute buffer before coffee is still the standard guidance. Consistency matters more than perfection here: taking your dose the same way every day keeps your levels predictable and makes dose adjustments more reliable.